To design an agricultural formulation product, the most important question to be answered is its stability. Failure to meet a set of stability requirements which usually depend on the specific market, application and regulations will certainly lead to failure of its commercialization. There are many causes of formulation instabilities, such as a) chemical instabilities due to reactions between ingredients (actives and/or inerts, etc.), photo-degradations, and oxidations, etc., b) physical instabilities due to phase separations (Oswald ripening, crystallization, sedimentations, creamings, etc.) and c) environmental factors (temperature, humidity/moisture, etc.). In today's agrochemical market, it becomes increasingly common to design formulations to contain multiple active ingredients and their required solvents, safeners, and/or adjuvants, etc., in order to achieve the optimal spectrum, efficacy, and delivery efficiency, which consequently makes formulation stability more and more challenging. Therefore, technologies that can effectively isolate, hinder, or eliminate, adverse reactions or interactions between incompatible ingredients are often critical for a successful product.
The emulsifiable concentrate, a liquid homogeneous formulation to be applied as an emulsion after dilution in water, is one of the most common formulation types for many agricultural products. Emulsifiable concentrates are mixtures of an oil-soluble active ingredient and emulsifying agents dissolved in an organic solvent. The emulsifying agent enables the emulsifiable concentrate to disperse easily in water, thereby forming a “milky” and homogenous emulsion. Emulsifiable concentrates require tank agitation to form the emulsion and maintain it during spraying. However, many challenges may exist, when, for instance, active ingredients may react with one another or with other ingredients in the formulation. For example, a composition containing triclopyr butoxyethyl ester and aminopyralid acid or its potassium salt has been found to be extremely useful for the control of brush and woody plants in range and pasture and industrial vegetation management applications. In some typical emulsifiable concentrate formulations with the hydrophobic ester herbicide and the hydrophilic acid or salt herbicide, only small amounts of the hydrophilic herbicide may dissolve in the organic solvent. In typical emulsifiable concentrate formulations with the hydrophobic ester herbicide and the hydrophilic acid herbicide dissolved in the oil phase, the acid herbicide may decarboxylate upon storage at elevated temperatures. In typical emulsifiable concentrate formulations with the hydrophobic ester herbicide and the hydrophilic salt herbicide dissolved in the oil phase, the hydrophilic salt herbicide may react with the oil-soluble ester herbicide, leading to hydrolysis or transesterification. It would be desirable to have a more stable emulsifiable concentrate containing a first herbicidal carboxylic acid in the salt form and a second herbicidal carboxylic acid in the ester form.